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Manual (HELP)

Soaring forecast background information


Model Sounding
The NAM or RUC Model Sounding (local sunrise) for the Current Day with the dry and wet adiabat based on the forecast maximum temperature and dew, will be shown.
 A verbal comment on the expected convection base height will be given.


Current Day
This is produced with Micromet, a program originally developed by the University of Cologne. The data is obtained from RAOBS soundings taken at 0000Z from stations upwind of the forecast area considering temperature/humidity and wind throughout the full vertical extent of the air mass where the sounding was taken.

Based on these soundings it calculates reverse trajectories of the movement of the air masses from the forecast area. When insufficient RAOB soundings are available, sounding data is obtained from area-specific computer model soundings. Additional data used are the actual early morning temperatures, dew point and the forecast maximum temperature for the area.

The program uses the annual and diurnal radiation for the forecast area and any cloud cover (which it calculates based on air mass humidity data) that influences it. The convection simulation assumes a 1.2 degree Celsius temperature difference compared to the surrounding air. It then considers dynamic entrainment, horizontal advection and turbulent entrainment of the rising air parcel. It also calculates condensation, raindrops and ice particle content.

Trajectories, Cloud Graph and Thermal Speed and Prognostic Sounding:


Trajectories 
Reverse Trajectories are shown in 1000m intervals (1000 to 7000m) toward the forecast area (center point). The outer end points of these lines show its origin and the flow of the air parcel from there to the center point in the forecast area  The colouring of the trajectories lines are darkest at the 1000m level and lightest at the 6000m level.

The program calculates between the time intervals with a constant airflow to the final point calculated from the surrounding stations through a distance weighted calculation. Hence following the trajectories it can be seen which adjective flows have influenced the forecast area. The trajectories give us a good idea where the air mass originates from and what characteristics it has.

For example, if the airflow is from the South it will be relatively warm air and most likely laden with moisture and pick up more moisture while moving across the Great Lakes. This type of air mass would reduce thermal activity due to warm air advection aloft.

But if the trajectories indicate an airflow from the North, it will be relatively cold dry continental air and because of this, it will not pick up any significant amount of moisture while moving over the Great Lakes to the West and North of our flying area. Such air would enhance thermal activity as it will bring in colder air aloft. 

Of course the airflow on the different levels will also give us an indication if it will be a good or bad soaring day, e.g. if the low level flow is from the South  , this will be relatively warm air and if the trajectories indicate the higher level flow northerly (cold air) it might increase instability and enhance thermal activity. If the airflow is reversed, cold air flowing in below and warm air above it will stabilize the air mass resulting in weak thermal activity.            

Cloud graph
Vertical column of numbers  is height above ground in thousands metres eg. 1 = 1000m etc)
First horizontal line of numbers  below graph is the temperature in deg C
Second horizontal line of numbers below graph is local time
Numbers in the graph above time/temp. is a meteorological lift rate in m/sec
If Lift rate only is shown it indicates Blue thermals
Cumulus clouds symbols,  size indicates small/large or towering
Straight lines indicates strati-form clouds
The dots `````````` indicate start of condensation height indicating  lowering visibility.
Line numbers along top of graph shows any high level clouds in eights of sky covered

Thermal Speed Graph
Vertical column of numbers (left side height above sea level in thousands metres (1 = 1000m etc)
Horizontal bottom column time interval 0 - 60 min indicating approximate duration of individual thermals.
Colour scale is met lift rate in m/sec (eg. dark blue =  1.8 - 2.9 m/s )

Prognostic Sounding is self-explanatory


C
omments

This section contains relevant information concerning , convection base, cloud type and cover, lift/climb rates, surface winds, visibility, and if required manually obtained adjustments to the computer forecast which the programs is unable to assess.

NOTES :

The Cloud Graph and the Thermal Speed graph show the meteorological (RAW) Lift rate . This is the expected rate of ascend of a parcel of air within the Convective Boundary Layer before Condensation without considering  the glider sink rate.

Comments shows the Average Indicated Climb Rate  based on the average Standard Class glider sink rate of 1.5 m/s (3kt)  at  45 deg. bank. 
The Meteorological (Raw) Lift Rate  is also shown for the individual pilot to deduct his own gliders assumed sink rate to arrive at an indicated climb rate.
1 m/sec  = 200 ft/min  = 2 kt

The Forecast is based on RAOBS taken at Midnight GMT   It considers up to  30 soundings taken upwind of the flying area, projecting the air mass overhead of the flying area for the time of the forecast period by applying reverse trajectories based on the strength of the airflow within the air mass.
This forecast is area specific, depending on the direction of the air flow it can be considered valid for an area between a 30 to 80km radius around the centre of the geographic position it was calculated for, in case of SW Ontario, the airfield of ARTHUR EAST is the centre of the area. For special events additional geographic positions might be used ( London,ON,Hanover,ON and Borden) to increase the forecast area. 

The program was developed specifically for predicting thermal conditions for soaring and is not to provide general weather forecasts. , Hence on days of active frontal passages  - 1. Current day  Graphs might not be posted.

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Additional Information for use of this forecast

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Frank Pennauer --
frpenn@gmail.com



2001 - 2017  Frank Pennauer / Web site: Sagitta Enterprise / Ellen Papenburg

Frank's Thermal Forecast